As they air their disagreements, the Republican presidential candidates agree on one thing: They want to repeal President Obama's health care law.

RENEE MONTAGNE, BYLINE: The biggest part of that law - a requirement that almost everybody must have insurance - does not take effect until well after the election. But any repeal effort would be complicated, because some of the law is already in effect.

INSKEEP: NPR's Julie Rovner is here to talk about how the law is changing the health care landscape. Hi, Julie.

JULIE ROVNER: Hey, Steve.

INSKEEP: OK, what's something that's in effect now?

ROVNER: Well, actually, a surprisingly large number of things are already in effect. For example, more than two-and-a-half million young people under the age of 26 are still on their parents' health insurance. Many, if not most of them, would probably be uninsured if not for the law.

INSKEEP: And under the old law you had to drop off your parent's health insurance at a younger age.

ROVNER: That's right, unless you were still in college. Millions of senior citizens are paying less for their prescription drugs. They are no longer falling into that notorious doughnut hole. And health insurers are now subject a lot of new consumer protection rules. For example, they have to spend 80 cents of each premium dollar on medical care itself rather than overhead, and if they don't, they have to give back rebates.

INSKEEP: So are several more million people actually insured today because of this law that passed in 2010?

ROVNER: Not that many more - that's the big part. It doesn't take effect until 2014.

INSKEEP: Is even more going to change before the election in November?

ROVNER: Not that much. This is actually a pretty quiet year. In 2012, really there's just a bunch of new rules for how Medicare is going to pay hospitals and other people who deliver health care. The real action comes next year in 2013, in preparation for 2014, which is when states have to be ready with these new insurance marketplaces called exchanges. That's where individuals and small businesses will be able to go to shop for health insurance. That's when more people will actually get insurance.

INSKEEP: OK. So how much progress are they making in setting up these exchanges?

ROVNER: Well, it's not going as fast as I think a lot of people had been hoping. You know, one of the reasons this law came with such a long lead time was to build essentially a whole new way of shopping for health insurance. And the way it's supposed to work is that states will either create their own exchanges or if they choose not to, the federal government will step in and do it for them. Right now there's two separate problems. First, you've got governors who do want to make this law work along with the Obama administration. They're finding this is just a really big, complicated job. Then you've got a lot of Republican governors who'd like to see the law go away, and they're dragging their feet on doing any of that real preparation in hopes that either the Supreme Court or a new president and Congress will actually make the law go away.

INSKEEP: And, of course, the Supreme Court is hearing challenges to the health care law. But I want to make sure that I understand what you say when you say health care exchanges. Because this is – is this basically a free enterprise idea? This is a new way to shop for different kinds of health insurance, is it fair to say?

ROVNER: That's exactly what it'll be. Now, if you already have health insurance through your job, you probably won't be involved in this. But for small businesses and for individuals who don't have health insurance or buy their own, they'll be able to get a choice of many different health insurance plans.

INSKEEP: Just to sum up here: You've said that several million people have been affected in one way or another by this. Behind the scenes, a lot of work is going on for bigger changes in the future. Is the law still at a point where you could simply reverse course, go back to the way things were before 2010?

ROVNER: Well, yes and no. Now, remember, the Supreme Court is looking at whether this individual mandate for most people to have insurance is constitutional or not. Now, they could rule that unconstitutional, but everyone seems to think it's unlikely that even if they did that, that the entire law would then be ruled unconstitutional. And if a Republican president were to be elected and a new Republican Congress, there's talk of repealing the law. But this law is, for better or worse, estimated to save money. So they would probably have to come up with money to make that up. Plus, you've got a lot of businesses and health providers who've done a lot of preparation work to make this law go into effect. They are not going to be so happy if this entire law is then reversed.

INSKEEP: Mitt Romney, the leading Republican presidential candidate, has been saying on the stump that this law is costing $95 billion per year. You're saying that simply repealing it would actually cost money. You'd have to go find money somewhere...

ROVNER: According to the Congressional Budget Office, which is the official arbiter that Congress has to obey, it would save money. So repealing it, they would have to find money.